Assuming that there is memory to spare, caching all, or part of Firefox's profile to RAM using tmpfs offers significant advantages. Even though opting for the partial route is an improvement by itself, the latter can make Firefox even more responsive compared to its stock configuration. Benefits include, among others:

reduced disk read/writes

heightened responsive feel

many operations within Firefox, such as quick search and history queries, are nearly instantaneous

Method 1: Use RAM-only cache

Firefox can be configured to use only RAM as cache storage. Configuration files, bookmarks, extensions etc. will be written to harddisk/SSD as usual. For this

open about:config in the address bar

set browser.cache.disk.enable to "false" (double click the line)

set browser.cache.memory.enable to "true" (double click the line)

set browser.cache.memory.max_entry_size to the amount of KB you'd like to spare, to -1 for automatic cache size selection

Main disadvantages of this method are that your tabs won't survive a browser crash, and that you need to configure the settings for each user individually. On the other hand on a personal system it probably is the easiest method to implement.

Method 2: Use PKG from the AUR

Relocate the browser profile to tmpfs filesystem, including /tmp for improvements in application response as the the entire profile is now stored in RAM. Another benefit is a reduction in disk read and write operations, of which SSDs benefit the most.

Use an active management script for maximal reliability and ease of use. Several are available from the AUR.

The script

The script will first move Firefox's profile to a new static location, make a sub-directory in /dev/shm, softlink to it and later populate it with the contents of the profile. As before, replace the bold sections to suit. The only value that absolutely needs to be altered is, again, xyz.default.

Be sure that rsync is installed and save the script to ~/bin/firefox-sync, for example: